Soil Solution pH Research Articles

Release Pattern of Dissolved Silicon and Its Budgeting under Rice Planted and Unplanted Condition in Acidic, Neutral and Alkaline Soils

ABSTRACT Release of silicon (Si) from different Si sources and Si budgeting in varied types of soils are required for the exploration of sustainable rice production. Si products are shown to be effective in improving crop growth and yield; however, its reactivity differs based on the soil type. A pot experiment was conducted by using three Si sources (calcium silicate (CaSiO3), diatomaceous earth (DE), and rice husk biochar (RHB)) in acidic, neutral, and alkaline soils under rice planted and unplanted conditions for a single season. A large variation in Si uptake by rice existed amongst the different sources of Si and was found to be higher in neutral soil followed by acidic and alkaline soil. Application of calcium silicate followed by diatomaceous earth recorded higher Si uptake in acidic (547.17 ± 39.15 mg pot−1) and neutral (632.65 ± 112.21 mg pot−1) soil whereas, rice husk biochar in alkaline soil (35.32 ± 4.60 mg pot−1). Application of calcium silicate and RHB significantly increased the plant available Si in post experimental soil. The soil solution pH of acidic, neutral and alkaline soils ranged from 5.62– 8.59, 6.62– 9.13, and 7.64– 9.37, respectively, with the application of different rates and sources of Si during the experimental period. The application of CaSiO3 followed by RHB increased the dissolved Si in acidic and neutral soil whereas RHB and DE in alkaline soil. The amount of DSi with the application of different sources and levels of Si ranged from 47– 447, 139– 751, and 161– 374 µmol L−1 in acidic, neutral, and alkaline soil, respectively. About 16 to 28% of Si in acidic and neutral soil and 10 to 19% Si in alkaline soil was accounted by irrigation water.

Residual effects of calcium amendments on oil palm growth and soil properties

Residual liming is one of the measures of the efficacy of liming materials. Ca2+-amendments such as calcium hydroxide (Ca(OH)2), calcium oxide (CaO) and calcium carbonate (CaCO3) in soils may contribute to plant growth response in plant height and total dry matter yield of oil palm seedlings. The increasing of other essential elements such as nitrogen (N), phosphorus (P) and ions of potassium (K+) also play a great role in the plant growth and crop yield, conversely, the soil pH and ions of aluminium (Al3+) will inhibit the plant growth and crop yield. This main aim this experiment is to determine the residual liming effect of Ca2+-amendments to highly acidic soils collected from Jeram and Bungor series, Malaysia, which also contains 2 times of Al3+. The highly acidic soils of previously planted with oil palm seedlings initially incubated with selected Ca2+-amendments along with Mg2+-amendments such as, dolomite (CaMg.CO3) for 360 days and, kept for additional 180 days before planting for a total of 540 days in a greenhouse environment. In this experiment, the soil chemical analysis, plant growth response, and the possible mechanisms responsible for the Ca2+-amendment liming effects were measured. The results of the soil chemical analysis showed that Ca2+-amendment residues potentially reduced the soil acidity than Mg2+-amendments. Ca(OH)2 was the most prominent Ca2+-amendment to increase soil-water pH, soil solution pH, and concentrations of soluble Ca2+ and K+. While, concentration of soil solution and exchangeable Al were effectively reduced 540 days after the application of Ca-amendments. The dry shoot weight of the oil palm seedlings improved about 1.67 g/pot and 16.87 g/pot in control and Ca2+-amendment treatments, respectively. In this study, it has showed that the root dry weight of oil palm seedlings increased from 0.18 g/pot to 4.49 g/pot in pot and Ca2+-amended soil, respectively. Increased plant height and total dry matter yield of oil palm seedlings grown on the Ca-amended soils may be attributed to increased soil pH which resulted in lowered concentration and activity of soluble AI, and increased concentrations of soil solution Ca and K which were released of Ca. This finding concluded that the possible mechanisms of Ca2+-amendments from residual liming might be: a) complexation interaction between Al3+ and Ca2+; (b) capacity of Ca-amendments to increase the concentration of Ca to maintain soil desired pH; (c) alleviation effect of Ca-amendments to reduce Al toxicity concentration in the soil. Last but not least, this finding showed that dry matter yield and plant height positively associated with the presence of Al3 + in both soil conditions.

Variability of soil mineralogical composition in Sentra Bareh Solok paddy field as affected by eruption material from Mt. Talang

Mt. Talang is one of the active volcanoes in West Sumatra with the last eruption occurred in 2017. The Sentra Bareh Solok paddy field distributed from volcanic middle slope to Singkarak Lacustrine Plain. The composition of sand mineral fraction of nine representative of soil profiles has been analysed using polarization microscope with line counting method. Results show that mineralogical composition are the same, but the amount are different. At the volcanic middle slope, opaque is dominant. It is probably due to thermal formation associated with the melting of existing iron oxides attributed by lava flow. Labradorite and hypersthene are dominant in Alluvial Plain and it could indicate rather slow weathering processes. While, the soils at Lacustrine Plain were dominated by volcanic glass and labradorite and it could be due to silica saturation; more cations and higher pH of soil solution hindering dissolution of minerals. The K-bearing minerals were absent in all soils, indicating K would be the problem as revealed by low K content and its trend decreased from middle slope to the lacustrine. The implication is soils in the Lacustrine Plain and Alluvial Plain would need more K fertilizers than soils in the middle slope.

Soil solution fluxes and composition trends reveal risks of nitrate leaching from forest soils of Italy

Although acidification is a natural soil formation process, atmospheric emissions of nitrogen and sulphur have exposed forest ecosystems to accelerated anthropogenic acidification for many decades. In Italy nitrogen deposition loads are high, and among the highest in Europe. Data from the Italian ICP-Forests monitoring network have shown that nitrogen deposition increases tree growth, and consequently the organic carbon sequestration. However, the accumulation of nitrogen in the ecosystem could cause nutrient imbalances and contribute to soil acidification. Within this context, we investigated the temporal changes of atmospheric deposition and soil solution concentration in the Italian ICP-Forests using the non-parametric Seasonal Mann Kendall (SMK) test. Further, we applied input–output models, to evaluate the capabilities of the soil-forest system to retain deposited nitrogen and thus protect underground waters.Increase of soil solution pH was observed in most of the sites, likely due to sulphate deposition decrease with a concomitant high and stable natural exchangeable base deposition. For the sites around the Po plain, however, high levels of nitrogen deposition impede pH increase. The site with the maximum mineral N deposition showed signs of active acidification. The analysis of the fluxes of nitrogen compounds demonstrates a complete retention of the ammonium forms, which further contribute to acidification through nitrification. Furthermore, the Italian monitoring network showed that the retention of nitrogen in the soil-forest system was effective since the observed N fluxes in mineral soil were strongly reduced compared to mineral N input in most of the plots. In spite of this, significant NO3- fluxes from the subsoil were observed in sites with high deposition, and also in the southernmost site which is exposed to relatively low mineral N loads. Drivers other than pollution should also be considered since N can follow different pathways at different time scales, influencing N leaching independently from the amount of deposition.

Dissolution of copper oxide nanoparticles is controlled by soil solution pH, dissolved organic matter, and particle specific surface area

Dissolution is the primary process affecting the bioavailability and toxicity of nanoscale copper oxide (nano-CuO) to plants and soil organisms. In this study, particle morphology, organic acid, and soil properties were considered to understand the dissolution characteristics of nano-CuO in soil solutions. The results showed that the copper ions (Cu2+) released from spherical nano-CuO (CuO NPs), tubular nano-CuO (CuO NTs), and spherical microsized CuO (CuO MPs) in the ten soil solutions were 26.6–4194.0 μg/L, 4.90–217.1 μg/L, and 10.8–326.0 μg/L, respectively. The concentration of Cu2+ was negatively correlated with the pH of the soil solution and positively correlated with the contents of dissolved organic carbon (DOC), aluminum, and manganese. Multivariate stepwise regression analysis indicated that the dissolution of CuO NPs could be well predicted by pH and DOC contents of the soil solutions. In the GD soil solution (acidic), 4- and 8-fold of the DOC content amendments significantly promoted the dissolution of the three sizes of CuOs, resulting in an increase of Cu2+ 4.55–11.3 and 5.67–16.2 times, respectively. In the CQ soil solution (neutral), 8-fold DOC amendments increase the release of Cu2+ 2.13–16.6 times. While in the SD soil solution (alkaline), promoting effect on the dissolution was only observed for nano-CuOs, with Cu2+ elevated by factors of 1.56–4.64 and 1.38–4.48. The amendments of Al3+ and Mn2+ in soil solution increased the amounts of Cu2+ 1.13–4.80 and 1.02–1.46 times in the GD soil solution. In comparison, no significant promoting effects were observed in CQ and SD soil solutions due to their stronger buffering capacities. These findings offer insight into the dissolution behavior of nano-CuOs in soils and be helpful to evaluate their environmental risks.

氮添加对亚热带常绿阔叶林土壤溶液化学特性的影响

土壤溶液被称作"土壤的血液"，是土壤中各种生物化学反应的中介物质，在外界环境发生变化时，土壤溶液化学成分能在其他土壤指标尚无变化之前对环境变化做出迅速响应。为了探索持续增加的大气氮（N）沉降对森林生态系统的影响，以华西雨屏区亚热带常绿阔叶林为对象，设置对照（CK，0 g m^-2 a^-1），低N（LN，5 g m^-2 a^-1），高N（HN，15 g m^-2 a^-1）三种N处理，通过人工施加硝酸铵（2017年9月起改施硝酸钠及氯化铵）的方法模拟N沉降增加情景，N处理42个月后，使用负压土壤溶液采样器定位收集A层（37-45 cm）及B层（52-60 cm）土壤溶液，并进行分析（每月1次，为期1 a）。结果表明：对照处理中A、B两层土壤溶液NO₃^-浓度达（3.94±0.77）mg/L、（4.27±1.13）mg/L，N添加显著提高两层土壤溶液NO₃^-浓度和B层NH₄⁺浓度；N添加显著降低土壤溶液pH，且显著增加Al³⁺浓度，Ca²⁺和Mg²⁺含量有增加趋势，但影响不显著；N处理使A层土壤溶液可溶性有机碳（DOC）浓度显著降低，对两层土壤溶液芳香化指数（AI）无显著影响；两层土壤溶液电导率（EC）及氧化还原电位（Eh）显著增加；此外，两层土壤溶液中许多化学成分均呈现极显著相关，特别是NO₃^-与EC相关系数达到了0.855。本研究中，对照处理极高的NO₃^-含量以及B层土壤溶液硝酸盐浓度高于A层，表明该亚热带常绿阔叶林N的有效性超过植物和微生物的总营养需求而发生淋溶，该生态系统已达到氮饱和状态，此外N添加会显著促进土壤酸化和铝离子活化，表层土壤溶液DOC的降低一定程度反映了凋落物分解受N添加的抑制作用，显著升高的氧化还原电位可能导致土壤中某些金属元素的迁移率降低。;Soil solution is called soil blood, which is the medium of various biochemical reactions in the soil. When the external environment changes, the chemical composition of the soil solution can quickly respond to the environmental changes before other soil indicators have changed. In order to explore the impact of increasing atmospheric nitrogen (N) deposition on forest ecosystems, we set up three N treatments including the control (CK, 0 g m^-2 a^-1), low N (LN, 5 g m^-2 a^-1), and high N (HN, 15 g m^-2 a^-1) in a subtropical evergreen broad-leaved forest in the raining area of west China, artificially applied ammonium nitrate to simulate the increase of N deposition (replaced with sodium nitrate and ammonium chloride since September 2017). After 42 months of N treatment, soil solution from two soil layers (layer A:37-45 cm, layer B:52-60 cm) was collected using negative pressure soil solution sampler and analyzed chemical composition once a month for a year. In CK, soil solution NO₃^- concentration reached (3.94±0.77) mg/L(layer A) and (4.27±1.13) mg/L(layer B). Nitrogen additions significantly increased soil solution NO₃^- and NH₄⁺ concentration in layer B. Nitrogen additions significantly reduced soil solution pH value and increased Al³⁺ concentration, and the concent of Ca²⁺ and Mg²⁺ increased with no significant in statistics. Nitrogen treatment significantly reduced the dissolved organic carbon (DOC) concentration in layer A, and had no significant effect on the aromatic index (AI) of soil solution in the two layers. The electrical conductivity (EC) and the redox potential (Eh) of soil solution increased significantly in two soil layers. In addition, many chemical components in the soil solution of two layers had extremely significant correlation, especially the correlation coefficient between NO₃^- and EC reached 0.855. In this study, the extremely high NO₃^- concentration in CK and higher NO₃^- concentration in layer B than in layer A indicated that the nitrogen availability of the subtropical evergreen broad-leaved forest exceeded the total nutrient requirements of plants and microorganisms, and the ecosystem had reached the state of nitrogen saturation. In addition, nitrogen addition significantly promoted soil acidification and aluminum activation. The decrease of DOC in surface soil solution to some extent reflected the inhibition of litter decomposition by nitrogen addition. The significant increase of redox potential may lead to the decrease of the mobility of some metal elements in the soil.

Mitigation of soil salinization and alkalization by bacterium-induced inhibition of evaporation and salt crystallization

Soil salinization and alkalization is one of the most devastating environmental problems, threatening the sustainable development of agriculture. Bio-amelioration using microorganisms such as bacteria is a promising method for the remediation of calcareous sodic and saline-sodic soil due to its high efficiency, low cost and environmental-friendly characteristics. In the present study, a salt resistant bacterium, Bacillus subtilis BSN-1, was isolated from arid region in Xinjiang, China, and its effects on salt crystallization during evaporation crystallization of saline-alkali soil solution were examined. It was found that the fermentation products of B. subtilis BSN-1, such as glutamic acid, significantly lowered the pH of saline soil solution because of the ionization of carboxyl. The complexation between Ca2+ and fermentation products inhibited the precipitation of Ca–P compounds as well, since the binding sites supplied for Ca2+ is one or two orders of magnitude than that for HPO42−. Moreover, the increased content of active phosphate is attributed to the chelation and adsorption exerted through carboxyl and amide bonds. These findings demonstrated that Bacillus subtilis BSN-1 suppressed the crystallization of phosphate and therefor increased the content of active phosphate, which may provide a promising solution for amendment and remediation of saline-alkali soil.

Intrinsic soil property effects on Cd phytotoxicity to Ligustrum japonicum ‘Howardii’ expressed as different fractions of Cd in forest soils

A better comprehensive understanding of the influence of soil/solution properties on cadmium (Cd) phytotoxicity is essential for soil Cd ecological risk assessment. The toxicity of soil spiked Cd to Ligustrum japonicum ‘Howardii’ seedling growth was conducted by the greenhouse pot experiments using 13 typical forest soils selected from mainland of China. The results showed that the ranges of Cd toxicity thresholds of 10% seedling growth inhibition (EC10) and 50% inhibition (EC50) followed the order: soil pore water Cd (EC10 on average 0.88 mg L−1 with the variation of 54.9 folds and EC50 on average 2.28 mg L−1 with variation of 41.8 folds), DTPA extractable Cd (EC10 on average 5.4 mg kg−1 with 20.9 folds variation and EC50 on average 17.86 mg kg−1 with 6.6 folds variation), total added Cd (EC10 on average 6.55 mg kg−1 with 16.7 folds variation and EC50 on average 22.11 mg kg−1 with 5.1 folds variation), which suggested that whatever the available Cd expressed, its toxicity is largely affected by soil properties. The empirical multiple equations were well developed between different fractions of Cd toxicity thresholds ECx (x = 10 or 50) and soil/solution. The results also showed that the pH inversely correlated with EC10 (r2 = 0.54, P < 0.01) and EC50 (r2 = 0.63, P < 0.001) based on soil pore water, indicating the ECx decreased with more toxicity as pH increased. No single significant soil solution properties were found for ECx in DTPA extractable Cd. For the ECx of DTPA extractable and total Cd, the content of aluminum oxides in soil and soil pH were the two significant factors inversely related with ECx, which explained 68%–79% of the inter-soil variation, respectively. Overall, soil or solution pH was the most important factor controlling Cd toxicity thresholds. Meanwhile, significant negative correlations existed between the soil solution pH and the slopes of parameter (b) of the dose-response curves for different fractions of Cd, implying that the growth of toxic effect enhanced as unit Cd dosage increased in low pH soils. These results will be helpful to evaluate the metal ecological risk in forest soils.

Nitrogen induced DOC and heavy metals leaching: Effects of nitrogen forms, deposition loads and liming

Atmospheric nitrogen (N) deposition is believed to accelerate dissolved organic carbon (DOC) production and could lead to increased heavy metal mobility into water resources. We sampled intact soil cores from the Isle of Skye with low background N deposition history and having Serpentine rock known for its higher heavy metal concentrations including zinc (Zn), copper (Cu), nickel (Ni) and lead (Pb). The effects of 16 (16kgN) and 32 kg N ha−1 year−1 (32kgN), and liming with 32kgN (32kgN+Lime) on soil solution chemistry and heavy metal mobilization were investigated over the 15-month study. Nitrogen in deposition load was added at five ammonium (NH4+) to nitrate (NO3−) ratios of 9:1, 5:1, 1:1, 1:5 and 1:9 along NO3−dominance. We found significant effects of load on Cu and NH4+/NO3− ratio on pH, DOC and Zn in soil solution. However, under lime and ratio experimental factors, liming significantly influenced pH, DOC, Cu and Pb, and NH4+/NO3− ratio pH, DOC, Ni and Zn whereas interactions between lime and ratio was significant for Ni and Cu. pH and DOC increased with N load, liming and NO3− dominance, and both correlated significantly positively. Liming under NH4+ dominance enhanced DOC production due to supply of base cations in lime. Mobilization of Cu, Ni and Pb was driven by DOC concentrations and, therefore, increased with load, liming and NO3− dominance in deposition. However, in contrast, low pH and high NH4+ dominance was associated with Zn mobilization in soil solution. On the contrary, despite of some patterns, heavy metals in soil HNO3 extracts were devoid of any load, lime and NH4+/NO3− ratio effects. Our study suggests that the effects of N load and forms in deposition on sites with high accumulated loads of metals need to be better quantified through soil solution partitioning models.

STUDY OF SOURCE MATERIAL FOR EDAPHIC SELECTION OF ALFALFA

The study of collectible samples of alfalfa of different ecological and geographical origin on the harvest of dry matter and seeds against the background of increased acidity of soil solution (pH 5.20-5.53) made it possible to highlight the promising beyond these indicators samples that can be used in further breeding work. Comparison of the height of alfalfa plants in the first slope and feed productivity in general for 2019 shows that there is no direct correlation between these values. For example, the Galaxie variety, which was itself visopory and exceeded the standard by 12cm, was only in fourth place for the dry crop, and the Olga and Media varieties, which exceeded the standard by 9cm, were only eighth and seventh in the dry material. However, for the selection of varieties that combine these two traits, donors may be samples that behind the harvest of dry matter and the height of plants for three years of research reliably exceeded the standard: Banat, Vavilovka (Rodnichok), Feraks 58, Galaxie and Ferax 28. Not all samples form the maximum of green mass in the first slope, so there is no definite pattern between the height of plants in the first slope and the collection of dry matter for the entire growing season. The highest yield of dry matter on average for three years of research was obtained from varieties Vavilovka (Rodnichok) (Ukraine) (1.42 kg/m2), Banat (Serbia) (1.36 kg/m2) and Posevnaya 3022 (Uzbekistan) (1.22 kg/m2) at the harvest of the Sinyuha-standard grade 1.08 kg/m2. The best in seed productivity were samples of Jidrune (Lithuania) (31.9 g/m2), Feraks 58 (Canada) (29.9 g/m2), Tibet (Kazakhstan) (28.5 g/m2), Radoslawa (Ukraine) (28.2 g/m2), Kishvardi 27 (Hung.) (27.7 g/m2), Olga (26.5 g/m2) and Vavilovka (Rodnichok) (Ukraine) (26.2 g/m2) with a yield of standart of 23.5 g/m2. Particular attention is paid to the variety Ferax 58 (Canada), which for all the years of research reliably exceeded the standard for seed harvest and was at the level of the standard or exceeded it in the yield of dry matter. Further breeding work will use samples that reliably exceeded the standard for the average of three years of research for the collection of dry matter and the seed crop respectively: Ferax 58 (10% and 27%), Radoslawa (7% and 20%), Olga (11% and 13%), In addition, these samples exceeded the standard for plant sisoin in the first slope in 2019 by 31%, 11%, 8% and 55%, respectively. Key words: alfalfa sowing, selection, sample, variety, dry matter crop, seed harvest.

Near-neutral pH corrosion of mill-scaled X-65 pipeline steel with paint primer

The corrosion behaviour of mill-scaled X65 pipeline steel with and without a primer layer was studied in a simulated near-neutral pH soil solution. Results revealed a three-stage corrosion process of the mill-scaled pipeline steel surface. The first stage included an initial preferential dissolution of goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) in mill scale. The second stage was marked by enhanced localized corrosion and pit-formation because of either galvanic corrosion or acidic dissolution in areas enclosed by mill scale. The final stage was general corrosion after the mill scale flaked off the steel surface. When the primer layer was applied, localized corrosion was significantly enhanced on the steel surface and persisted for an extended period as compared to the mill-scaled condition. The precipitation of siderite (FeCO3) was observed at flawed locations of mill scale, although the bulk chemistry is not favorable for its formation on the steel surface free of mill scale. The local precipitation of siderite formed a capped mill scale enclosure where localized corrosion can be further enhanced.

Lead immobilization processes in soils subjected to freeze-thaw cycles.

Soil freeze-thaw cycles (FTCs) change the physical and chemical properties of soils; however, information is limited about the consequences for heavy metal sorption and desorption. Lead (Pb) sorption isotherms and successive desorption tests were measured for three soils from North China (Chestnut, Lou and Black), following multiple freeze-thaw cycles (0, 1, 3, 6 and 9 FTCs) of -5°C for 12h and then +5°C for 12h. Lead adsorption dominated the sorption processes for all soils, and sorption capacity increased with additional FTCs. The Freundlich affinity parameter of soils for Pb sorption (i.e. A; Lβ mmol1-β kg-1), was linearly correlated with carbonate content for soils with multiple FTCs. The effects of FTCs on lead adsorption may be more dependent on carbonate and clay contents than organic matter (OM), cation exchange capacity (CEC) and amorphous iron content. Repeated FTCs increased the pH of soil solutions at applied Pb concentrations >1.4mmolL-1, which could facilitate formation of inner-sphere complexes of Pb in studied soils. Cation exchange, a weak association, could occupy specific adsorption sites with increasing Pb doses in soils and it can also be facilitated by FTCs. Our results demonstrate the great potential for increasing Pb immobilization with repeated FTCs, by facilitating the formation of both inner-sphere and outer-sphere complexes. Hence, these findings provide useful information on Pb immobilization in contaminated soils that undergo frequent FTCs and offer an additional insight into predicting Pb behavior in cold and freezing environments like the polar regions.

Importance of soil interparticle forces and organic matter for aggregate stability in a temperate soil and a subtropical soil

Soil organic matter (SOM) and interparticle forces, including the electrostatic repulsive force (ERF), surface-hydration repulsive force (SHRF) and van der Waals attractive force (vDWAF), play crucial roles in aggregate stability. However, few studies investigated their coupled effects on aggregate stability in variably charged soils, in which soil particle interactions are more complex than in permanently charged soils due to the coexistence of positive and negative charges and the variable surface charge characteristics. Therefore, this study aims to: 1) investigate the combined effects of soil solution pH and the overlapping of electric double layers (EDLs) between positively charged Fe/Al (hydro)oxides and negatively charged SOM on the ERF and aggregate stability before (control) and after SOM removal and after straw incubation for 240 days; and 2) evaluate the importance of soil interparticle forces and SOM for aggregate stability in a permanently charged temperate soil (Vertisol) and a variably charged subtropical soil (Ultisol). Soil aggregate stability was determined by measuring the release of small particles (w(<d)%) after aggregate breakdown at different KCl concentrations (10−1 to 10−5 mol L−1). Soil solution pH was adjusted by varying KCl concentration. In both soils, the w(<d)% increased exponentially with the net force of the soil interparticle forces. However, in contrast to the Vertisol, the w(<d)% of the differently treated Ultisol showed almost no change before the KCl concentration decreased to 10−2 mol L−1 and continuous changes after the KCl concentration decreased to 10−2 mol L−1. In addition, the differences in the w(<d)% between the SOM removal treatment and the control and straw incubation treatments were much larger in the Ultisol than in the Vertisol. In the Ultisol, the ERF did exhibit little and continuous increase over the whole range of tested pH. When considering the impact of the overlapping of oppositely charged EDLs between Fe/Al (hydro)oxides and SOM, a much stronger reduction in ERF was observed in the control and straw incubation treatments and at lower KCl concentrations. Consequently, in both the Vertisol and Ultisol, aggregate stability is essentially controlled by the soil interparticle forces, whereas the effects of soil solution pH and the overlapping of oppositely charged EDLs between SOM and Fe/Al (hydro)oxides on the ERF must be considered in variably charged soils (i.e. Ultisol). Moreover, SOM can play a more important role in aggregate stability in subtropical soil than in temperate soil.

Microbial driven iron reduction affects arsenic transformation and transportation in soil-rice system

The microbe-driven iron cycle plays an important role in speciation transformation and migration of arsenic (As) in soil-rice systems. In this study, pot experiments were used to investigate the effect of bacterial iron (Fe) reduction processes in soils on As speciation and migration, as well as on As uptake in soil-rice system. During the rice growth period, pH and electrical conductivity (EC) in soil solutions initially increased and then decreased, with the ranges of 7.4–8.8 and 116.3–820 mS cm−1, respectively. The concentrations of Fe, total As and As(III) showed an increasing trend in the rhizosphere and non-rhizosphere soil solutions with the increasing time. Fe concentrations were significantly positively correlated with total As and As(III) concentrations (***p < 0.001) in the soil solutions. The abundances of the arsenate reductase gene (arsC) and the As(III) S-adenosylmethionine methyltransferase gene (arsM) in rhizosphere soils were higher than those in non-rhizosphere soils, while the abundance of the Fe-reducing bacteria (Geo) showed an opposite trend. Moreover, it showed that the Geo abundance was significantly positively correlated with that of the arsC (***p < 0.001) and arsM (**p < 0.01) genes, respectively. The abundances of Geo, arsC and arsM genes were significantly positively correlated with the concentrations of Fe, total As and As(III) in the soil solutions (*p < 0.05). Moreover, the abundances of arsC and arsM genes were significantly negatively correlated with total As and As(III) in rice grains (*P < 0.05). These results showed that the interaction of bacterial Fe reduction process and radial oxygen loss from roots promoted the reduction and methylation of As, and then decreased As uptake by rice, which provided a theoretical basis for alleviating As pollution in paddy soils.

Predicting Cr(vi) adsorption on soils: the role of the competition of soil organic matter.

Cr(vi) has posed a serious risk for the environment and human beings because of its pollution and toxicity. It is essential to understand the equilibrium behavior of Cr(vi) in soils. In this study, the adsorption of Cr(vi) on fourteen soils was studied with batch experiments and quantitative modeling. The batch experiments included the adsorption edge and adsorption isotherm experiments, investigating the adsorption of Cr(vi) with varying soil properties, solution pH, and initial Cr(vi) concentrations. The experimental data were then modeled using the surface complexation models in Visual MINTEQ of CD-MUSIC by considering the adsorption of Cr(vi) and ions onto Fe (hydr)oxides and Al (hydr)oxides, and the Stockholm Humic Model and the fixed charge site model by accounting for the adsorption of the cations to soil organic matter and clay, respectively. Particularly, the modeling method of this study introduced an important parameter RO- to account for the amount of soil organic matter irreversibly adsorbed on soil minerals. Overall, the model predicted reasonably well for the equilibrium partition of Cr(vi) under various conditions with a root-mean-square-error of 0.35 for the adsorption edge data and 0.19 for the adsorption isotherm data. According to the model calculations, ferrihydrite dominated the binding of Cr(vi) at pH of 3.0-7.0. The content of ferrihydrite and reactive soil organic matter was found to be the main factor influencing RO-. The modeling results help to understand and predict Cr(vi) adsorption on different soils and are beneficial to environmental risk assessment and pollution remediation.

ВИВЧЕННЯ ТА ДОБІР ВИХІДНОГО МАТЕРІАЛУ ДЛЯ СТВОРЕННЯ СОРТІВ І ГІБРИДНИХ ПОПУЛЯЦІЙ ЛЮЦЕРНИ ПОСІВНОЇ, ТОЛЕРАНТНИХ ДО ПІДВИЩЕНОЇ КИСЛОТНОСТІ ГРУНТОВОГО РОЗЧИНУ

The study of collecting samples of alfalfa of different ecological and geographical origin for the collection of dry matter and seed yield on the background of high acidity of soil solution (pH 5,20-5,53) made it possible to identify perspectives for these indicators that can be used in further breeding work. The highest dry matter yield in the average of 3 years of research was obtained from the varieties Vavilovka (Rodnich) (Ukraine) (1.42 kg / m2), Banat (Serbia) (1.36 kg / m2) and Sowing 3022 (Uzbekistan) (1,22 kg / m2) at the yield of the Sinyukh standard of 1.08 kg / m2. Seeds of Zhidrune (Lithuania) (31.9 g / m2), Ferrax 58 (Canada) (29.9 g / m2) and Tibet (Kazakhstan) (28.5 g / m2) with yield of standard 23.5 g / m2 were the best seeds. Particularly noteworthy is Ferrax 58 (Canada), which has significantly exceeded the standard of seed yield and exceeded or exceeded the standard of dry matter during all years of research.

Dynamics of soil acidity in the Steppe

The dynamics of the soil solution of agricultural lands in Kirovohrad region during five rounds of agrochemical examination was investigated. It is established that during 35 years the amount of close to neutral and slightly alkaline soils in Kirovohrad region has increased but acidic and neutral ones have decreased. Due to the intensive chemicalization of agricultural production in the 1970s and 1980s, 248,3 thousand hectares of deep and ordinary black soils were transferred to the category of acidic soils. It was found that the proportion of soils that have a weakly acidic reaction of soil solution (pH 5.1–5.5) decreased by 11.0%. Currently, the amount of acid soils has decreased and in 2015 amounted to 105,8 thousand hectares. The proportion of soil close to neutral (pH 5.6–6.0) increased significantly from 41.0 in 1995 (VI round) to 55.1% in 2015 (X round). In the redistribution of soils with neutral reaction (pH 6.1–7.0) there were slight changes from 36.6% in 2000 to 31.3% in 2015. Due to the sharp decline in the number of farm animals, the use of organic fertilizers decreased to a negligible amount of 0.1 t/ha (IX–X round). Mineral fertilizer volumes declined rapidly until 2000 and have gradually increased over the last 17 years. Thus, the application of mineral fertilizers in the region increased from 6.9 kg/ha up to 63.5 kg/ha of active substance. In order to reduce the share of acidic soils on agricultural lands in Kirovohrad region under the current conditions of agriculture it is necessary to: reduce the proportion of physiologically acidic mineral fertilizers; to use local agrochemicals, such as defecate, serpentinite, and calcareous metallurgical slag, for chemical reclamation.

Biodegradation of phthalate esters in four agricultural soils: Main influencing factors and mechanisms

Phthalate esters (PAEs) are among the frequently detected organic pollutants in agricultural soils. Here, we investigated adsorption and biodegradation behaviors of di-ethyl phthalate (DEP) and dibutyl phthalate (DBP) in the soils collected from four regions in China: Changchun (CC), Changsha (CS), Cangzhou (CZ), and Yinchuan (YC). The results demonstrated that soil organic matter content crucially influenced the adsorption progress. However, the calculated degradation rates of PAEs in the four soils had no significant correlation with their adsorption capacity, suggesting that PAEs' bioavailability might be not the limiting factor governing their degradation. Furthermore, homogeneous biodegradation experiments were performed in the soil solutions extracted from different regional soils. Results showed that biodegradation of PAEs was influenced by the soil solution's pH and its concentration of dissolved organic matter (DOM). To better understand the accelerating mechanism of DOM, bacterial growth and enzyme activity in the presence of Humic acid (HA) and Fulvic acid (FA) were determined, and the degradation of PAEs by intracellular enzymes were also investigated. These results suggested that HA, FA, and other forms of DOM were actively involved in this biodegradation process in two ways: namely, via nutritional support and sequestration of PAEs. We conclude that the actual impact of soil organic matter (SOM) upon PAEs' biodegradation in soils arose from the net outcome of these two opposing effects.

Assessment of the Role of Different Soil Properties on Crust Strength by Linear Regression Models

Soil crust strength influences seedling emergence, penetration and morphology of plant roots, and, consequently, crop yields. A study was carried out to assess the role of different soil properties on crust strength atHisar, Haryana, India. The soil samples from 0-5 and 5-15 cm depths were collected from 21 locations from farmer’s fields, having a wide range of texture.Soil propertieswere evaluated in the laboratory and theirinfluence on the modulus of rupture (MOR), which is the measure of crust strength, was evaluated.The MOR of texturally different soils was significantly correlated with saturated hydraulic conductivity at both the depths. Dispersion ratio was found to decrease with an increase in fineness of the texture of soil and the lowest value was recorded in silty clay loam soil,which decreased with depth. The modulus of rupture was significantly negatively correlative with the dispersion ratio.There was no role of calcium carbonate in influencing the values of MOR of soils. Similarly,the influence of pH, EC and SAR of soil solution on MOR was non-significant.A perusal of thevalues of the correlations between MOR and different soil properties showed that the MOR of soils of Haryana are positively correlated with silt + clay (r = 0.805) followed by water-stable aggregates (r = 0.774), organic carbon (r = 0.738), silt (r = 0.711), mean weight diameter (r = 0.608) and clay (r = 0.593) while negatively correlated with dispersion ratio (r = - 0.872), sand (r = -0.801) and hydraulic conductivity (r = -0.752) of soils.

Assessing cadmium availability of contaminated saline-sodic soils as influenced by biochar using the adsorption isotherm models

ABSTRACT In arid/semi-arid regions, soil salinization, sodification and contamination by heavy metals (HMs) are the main constrains to plant growth, crop production and human health. Biochar can affect soil behaviors, e.g. adsorption of HMs that is one of the most effective techniques for reducing their bioavailability. Effect of three levels (0%, 2% and 4% wt) of sugarcane bagasse-derived biochar and two cadmium (Cd) levels (0 and 50 mg Cd kg−1 soil as Cd(NO3)2) on Cd adsorption of saline, sodic, saline-sodic and normal soils were evaluated through studying adsorption isotherms. Six isotherm models were fitted to the data and the best model were chosen. The maximum Cd adsorption (694 mg kg−1) obtained in sodic soils without biochar treatment. Cadmium removal decreased when dosage of the applied biochar increased. The minimum Cd removal obtained as 17%, 21%, and 23% in control, 2% and 4% biochar-treated saline soils, respectively. Biochar increased Cd adsorption in salt-affected soils. Increasing pH in soil solution after biochar addition resulted in an increase in net negative surface charge and the affinity of soil particles for Cd adsorption. Consequently, 2% biochar could ameliorate Cd contamination. However, Cd adsorption decreased when dosage of the applied biochar increased from 2% to 4%.